The figure shows two crop fields [Plots $A$ and $B$] that have been treated with manures and chemical fertilizers,respectively,while keeping other environmental factors constant. Observe the graph and answer the following questions.
$(i)$ Why does plot $B$ show a sudden increase and then a gradual decrease in yield?
$(ii)$ Why is the highest peak in the plot $A$ graph slightly delayed?
$(iii)$ What is the reason for the different patterns of the two graphs?

(N/A) $(i)$ With the addition of chemical fertilizers,there is a sudden increase in yield due to the release of nutrients like $N, P, K$ in high quantities. The gradual decline in the graph may be due to the continuous use and high quantity of chemicals,which kill microbes useful for replenishing organic matter in the soil. This decreases soil fertility.
$(ii)$ Manures supply small quantities of nutrients to the soil slowly as they contain large amounts of organic matter. They enrich the soil with nutrients,thereby increasing soil fertility continuously.
$(iii)$ The difference in the two graphs indicates that the use of manure is beneficial for long-term cropping as the yield tends to remain high even when the quantity of manure increases.
In the case of Plot $B$,chemical fertilizers may cause various problems when used continuously for a long time. The loss of microbial activity reduces the decomposition of organic matter,and as a result,soil fertility is lost,which negatively affects the yield.